We just moved into our new place. So many new things need to learn. Just like the problematic AC. My apologizes if I do not know the correct terminology for some of the parts. I will try my best though.

The air handler with evaporator was installed in a closet on the 2nd floor. The evaporator is at the bottom in the air handler unit. And there is a big hole on the floor plywood right underneath the air handler to let the return air come in.

So the problem we have is that if we run the A/C for about 1.5 to 2 hours, we can see water drips to the ceiling of the first floor. And there is a water mark on the ceiling. So I just drilled a hole and let the water run down to avoid further damage. And I also took a picture through the hole to see what is going on(the filter has been removed). I saw condensate forming on the bottom of the drain pan. I'm not sure if the coil sweating.

What I've found/tested are:

The main drain pan seems working okay. I can see it catches water and
let it go away through the pipe to the drain-line. But the pan is
dirty. And it seems not overflowed.

Looks like there is no backup drain pan so the condensate drops
directly on the ceiling.

The filter is a washable filter and has been cleaned.

Tried to put a dehumidifier in the closed but didn't help too much.

I'm not sure what I can do next to fix this problem permanently. I thought I should install a secondary pan and clean the coil regularly. Am I on the right path? If you get an idea, please let me know.

@Tester101 Yes, I realize that now. It's definitely a poor design. I'm just looking for a reasonable way to improve it.
– Shey ShiJul 24 '15 at 19:42

1

I have exactly the same issue! I would love to hear if Shey Shi resolved the issue and if so, how? I read on the manufacturer's website (Bryant) that if the installation is on the first floor then a secondary drain pan must be installed. But the builder did not ensure that the contractor did so.
– user48615Feb 1 '16 at 15:45

@HemantPatel Sorry to hear that you have the same problem. Seems I'm not alone. I live in cold Canada. And summer is short in my province. So I didn't even get a chance to fix the AC last year. I'll have some professionals come in the summer and see if they can fix it. I'll keep you posted if I still remember. Please also let me know if yours is fixed. Good luck.
– Shey ShiFeb 2 '16 at 16:26

One of the A/C service companies I called said that I need a new evaporator coil. This may cost anywhere upwards of US$1200. I will get other estimates and keep you posted.
– user48615Feb 4 '16 at 4:04